Compressed gas guns operate to release a quantity of compressed gas into the breech of a barrel, which has been pre-loaded with a projectile, thereby propelling the projectile out of the barrel at a relatively high velocity. In practice, such a gun must provide a source of compressed gas in order to be operational. Typically, this source of gas is a tank which is pre-charged prior to being coupled with the gun or a fixed tank which is charged in place while coupled to the gun. In either case, the tank holds a finite quantity of compressed gas. Upon discharging the gun one or more times, the reserve of compressed gas is ultimately depleted and must be replenished.
In operation, the breech of the barrel must be accessible for inserting a projectile. If the gun is manually loaded, it is desirable to provide a readily accessible breech which can be conveniently loaded with the fingers of the user.
A valve mechanism is commonly provided which acts to discharge a quantity of compressed gas upon actuation of a trigger mechanism. However, prior to discharging the gun, the valve assembly must be coupled to the breech of the barrel in order to seal the gas port between the tank and the breech of the barrel. It is certainly desirable to provide a tight seal which serves to conserve the amount of gas consumed upon discharging the gun and also to conserve the pressure of the gas so as to maximize the amount of energy transferred from the compressed gas to the projectile. Furthermore, a tight gas seal reduces the sound level of the gun upon discharging, which is desirable in compressed gas guns.
The quantity of parts, particularly precision parts, is a factor in the cost of producing a compressed gas gun. Accuracy and repeatability of the projectile trajectory, upon firing, are desirable in compressed gas guns. Precision components and accuracy often go hand in hand. While some users view compressed gas guns as a sort of toy, there is a segment of the compressed gas gun market which demands the highest possible level of accuracy and performance in such guns. Indeed, compressed gas guns are used in competitive, hunting and other sporting events where accuracy, efficiency, and durability are of utmost importance. Compressed gas guns offer advantages over conventional fire arms, including the lack of any need for an operator's license, low operating cost, and quiet operation.
Various compressed gas guns have been proposed which accomplish the foregoing tasks involved in discharging such a gun. Many of the proposed designs utilize a large quantity of precision parts to produce a high quality gun. Often times, the trigger mechanism, valve assembly, and breech seal require the majority of precision parts. If a compromise is made in the quality of the design or parts, gun quality usually suffers.
The vast majority of compressed gas guns utilize a barrel which is rigidly fixed to the frame of the gun. This is viewed as desirable because the hand grips, barrel, and aiming sights are rigidly fixed in relation to each other. This is believed to provide a gun with repeatable accuracy. However, such guns do not lend themselves to a design which provides both a readily accessible breech and a tight seal in the compressed gas circuit. In order to accomplish this, a complex mechanism if often required, which usually increases the cost and decreases the durability and reliability of such guns.
A gun has been proposed which incorporates a movable barrel that is driven against a valve assembly upon actuation of a trigger mechanism. A cylindrical barrel is provided that includes a breech opening cut into the side of the barrel, near the breech end of the barrel. A valve stem extension is employed which extends a sufficient length out from the valve assembly so as to reach into the rear of the barrel a sufficient distance to pass the breech opening when the barrel is driven rearward to actuate the valve assembly. The gun suffers from several disadvantages which reduce the accuracy, efficiency, convenience, and reliability of the design.
Since the breech is cut into the side of the barrel and since compressed gas guns are usually of small caliber, it is difficult and inconvenient to load a projectile into the barrel. The cylindrical barrel is movable within a cylindrical opening formed into the frame of the gun. In order to provide ease of movement, the tolerance between the two must be loose, thereby allowing lateral play and reducing the accuracy of any gun of such design. The gas seal between the valve stem extension and the barrel is an `O`-ring which must slide against the bore of the barrel for most of the length of movement of the barrel, including sliding past the beech opening. This movement, combined with the lateral play of the barrel results in a seal which is prone to leakage, thereby increasing the quantity of compressed gas consumed and reducing the effective energy transfer from the compressed gas to the projectile. Further, gas leaks tend to increase the sound level of the gun upon discharging.
Another disadvantage of the prior art moveable barrel design is the tendency of the barrel to rebounds after actuating the valve assembly. When the barrel rebound after discharging, it re-impacts the valve assembly and may cause a subsequent actuation and release of gas, thereby wasting compressed gas and further increasing the sound level of the gun.
Clearly there is a need for a compressed gas gun which improves upon prior designs. Such a gun would offer ease of loading, quiet operation, accuracy, efficiency, and reliability. Further, such a gun would comprise relatively few parts, particularly precision machined parts, while still offering the foregoing advantages.